linux内核中的major（）和minor（）函数

Hi I'm running vfs_stat, fd is an opened file desciptor of /dev/tty0:

嗨我正在运行vfs_stat，fd是/ dev / tty0的打开文件说明符：

set_fs (KERNEL_DS);
if (vfs_fstat (fd, &stat))
{
    goto out3;
}

if (stat.mode & S_IFCHR)
    printk (KERN_INFO "opening %s (dev %d)\n", filename, stat.rdev);

And it prints:

它打印：

[ 8657.480625] opening /dev/tty0 (dev 4194304)

So now I need to retrieve major number of the device, but I couldn't find major() or minor() definition in linux kernel.

所以现在我需要检索设备的主要数量，但我在linux内核中找不到major（）或minor（）定义。

I found this answer but it doesn't seem to be right:

我找到了这个答案，但似乎不对：

#define major(dev) ((int)(((unsigned int) (dev) >> 8) & 0xff))
#define minor(dev) ((int)((dev) & 0xff))

Because if I do printk (KERN_INFO "opening %s (dev %d)\n", filename, major (stat.rdev)); The second field is always zero.

因为如果我做printk（KERN_INFO“打开％s（dev％d）\ n”，filename，major（stat.rdev））;第二个字段始终为零。

How should I get the major number then?

那我该怎么办？

1 个解决方案

#1

I found linux/include/linux/kdev_t.h which has:

我发现linux / include / linux / kdev_t.h有：

#define MINORBITS        20
#define MINORMASK        ((1U << MINORBITS) - 1)

#define MAJOR(dev)        ((unsigned int) ((dev) >> MINORBITS))
#define MINOR(dev)        ((unsigned int) ((dev) & MINORMASK))
#define MKDEV(ma,mi)      (((ma) << MINORBITS) | (mi))

Which seems "better" than the code you showed, since this has more bits allocated for the major number (20 rather than 8).

这看起来比你展示的代码“更好”，因为它有更多的位分配给主要数字（20而不是8）。

#1